Opel GT Forum banner
1 - 20 of 25 Posts

·
Registered
Joined
·
102 Posts
Discussion Starter · #1 ·
This posting is the most current chapter in the odyssey of my wife's GT. A quick catch-up: several weeks ago the ball stud backed off of the throttle shaft while my wife was cruising home on the freeway. The near miraculous finding of a zip tie on the shoulder of the freeway where she was stranded allowed me to MacGyver the linkage and drive the Opel home. About a week ago I installed the new ball stud from OGTS (along with a new linkage grommet) and the car is road worthy again. The problem is that its running a little rough and very rich. So..
First some background. Prior to acquiring the Opel, my shade tree mechanic-ing has centered around 60s - 70's Mopars during which time I've gained experience working on and tuning Edelbrock carbs. Between reading up on dozens of threads in this forum, YouTube, and downloading a Weber manual, I'm on my way to learning the Weber down draft carb. Pulling the plugs, all four were covered in black soot. Fortunately no oil fouling. I tuned the carb to best-lean-idle based on Redline's procedure but it didn't seem to make much difference. Next I pulled the air horn and measured the float settings. They read 35mm closed and 46mm open. I adjusted the floats to 36/50 per the Weber manual. The carb was really clean inside so I left everything else alone and buttoned it back up.
And now I'm getting to the reason for this post. Using my vacuum pump I tested the distributor diaphragms (its a 69 distributor with two pots plus Pertronix EI). The retard cannister held vacuum. The advance cannister bled down from 15" to 10" in 10 seconds; then slowed down from 10" to 5" in 40 seconds before settling at 5". The good news is that the advance weights rotated as vacuum was applied.
Come to find out that the usual sources - OGTS and Splendid don't sell cannisters or distributors, and eBay wasn't any help either. So where does one go to find replacement diaphragms, or worse case, distributors?
 

·
Registered
Joined
·
102 Posts
Discussion Starter · #2 ·
Two other questions related to the above.
As I understand, the external advance port on the carb is ported vacuum. Physically, the port is below the throttle blades so I'm assuming the port leads to an internal channel that exits above the blades. Is that correct?
The advance port is pulling 4" vacuum so as I understand the idle circuit is uncovered. Could have always been that way or maybe I uncovered it while doing the lean-best idle tune. Again, based upon my limited knowledge of how the Weber works, I assume the diaphragm has to be replaced before the advance port can be addressed.
Lastly, when I unplugged hose at the retard port on the manifold tree, the car died immediately. I assume that the port is full manifold vacuum and I created a massive vacuum leak that the idle circuit couldn't overcome.
I appreciate any input on how close or far-off I am on my assumptions. And also how to tackle the advance port vacuum leak.
Thank you.
 

·
Registered
Joined
·
1,060 Posts
Good job recording the before and after float settings. Since you have a vacuum pump. Check the operation of your full power valve. Take off the cover,
Do a quick read on Rallybob’s post #13
It could be responsible for the rich problem.
On the advance distributor canister if all else fails try Todd at Opels Unlimited, hopefully someone here has a spare advance canister and will save you the grief of the wait, he’ll come through but is usually slow in my experience. I’ll look when I get home to see what I have. Another person to try in our group is Opelmiester, he’s got a fair amount of used parts. Just look him up and send him a pm.

Post a couple of pics, one good one of the vacuum advance hose connection at the carburetor to see what your talking about, the other of the top of the distributor with the cap off. I’d encourage you to plug off the retard canister hose.
Check for vacuum leaks around the base of the carburetor & intake to head areas. It sounds like you have the throttle plates open too far, this also will cause a rich running car at idle.

Finally check for a wobble at your main throttle shaft on the carburetor. You may have worn an egg shaped grove on the carburetor base. If you get movement of the shaft where it’s going in to the carburetor you’ll be able to tell. Don’t forget to post the pics
 

·
Detritus Maximus
Joined
·
2,993 Posts
My experience is that a bad power valve leads to no idle mixture adjustment affect and the only way to get it to idle is to crack open the throttle (idle speed screw) and it idles at 1100 rpm, rather poorly, too.
 
  • Like
Reactions: Lil Red GT

·
Registered
Joined
·
102 Posts
Discussion Starter · #5 · (Edited)
Good job recording the before and after float settings. Since you have a vacuum pump. Check the operation of your full power valve. Take off the cover,
Do a quick read on Rallybob’s post #13
It could be responsible for the rich problem.
On the advance distributor canister if all else fails try Todd at Opels Unlimited, hopefully someone here has a spare advance canister and will save you the grief of the wait, he’ll come through but is usually slow in my experience. I’ll look when I get home to see what I have. Another person to try in our group is Opelmiester, he’s got a fair amount of used parts. Just look him up and send him a pm.

Post a couple of pics, one good one of the vacuum advance hose connection at the carburetor to see what your talking about, the other of the top of the distributor with the cap off. I’d encourage you to plug off the retard canister hose.
Check for vacuum leaks around the base of the carburetor & intake to head areas. It sounds like you have the throttle plates open too far, this also will cause a rich running car at idle.

Finally check for a wobble at your main throttle shaft on the carburetor. You may have worn an egg shaped grove on the carburetor base. If you get movement of the shaft where it’s going in to the carburetor you’ll be able to tell. Don’t forget to post the pics
When I had the airhorn off I wanted to look at the power valve however after removing the three screws it was still stuck to the gasket and wouldn't pop free; without a rebuild kit or spare gasket I didn't want to tempt fate so reinstalled the screws.
When taking a reading to measure idle vacuum, which port do you hook into?
Speaking of ports, the circled port is tied to the advance diaphragm and the one below with the blue arrow pointing to it ties into the retard diaphragm. (the electric choke wire was disconnected for the photo). I've read in other posts that members plug the retard diaphragm because it serves no purpose other than emissions control.
I'll have to take a closer look the throttle plates to see if they're cracked open. Thing is, the motor is idling at 850 so if I back off the idle screw to close the plates its going to run real rough. Likely a consequence of the bad diaphragm.
Motor vehicle Automotive tire Automotive fuel system Automotive wheel system Gas
Automotive fuel system Motor vehicle Car Coil Gas
 

·
Registered
Joined
·
102 Posts
Discussion Starter · #6 ·
My experience is that a bad power valve leads to no idle mixture adjustment affect and the only way to get it to idle is to crack open the throttle (idle speed screw) and it idles at 1100 rpm, rather poorly, too.
The motor idles at 850 although it can be smoother. What goes "bad" on a power valve?
 

·
Registered
Joined
·
102 Posts
Discussion Starter · #7 ·
BTW, another Weber question. While looking straight down at the top the carb, looking down the narrow "window" just behind jets I could see fuel puddling down below. After removing the top cover, I realized it was the float bowl. So the float bowl is open to the atmosphere? I've never seen that before.
Automotive fuel system Motor vehicle Gas Rim Auto part
 

·
Detritus Maximus
Joined
·
2,993 Posts
The motor idles at 850 although it can be smoother. What goes "bad" on a power valve?
I guess the first thing to say is that it's not really the power valve that goes bad. Technically the power valve is in the bottom of the fuel bowl and the part that typically fails is the rubber diaphragm on the actuating rod/spring. But it's still called the power valve.

The power valve diaphragm can get a crack or hole and won't hold vacuum.
When the motor is running the vacuum pulls the power valve actuating rod up off the valve letting the valve close. When you accelerate your vacuum decreases letting the rod lower and open the valve to enrich the fuel mixture (this is in addition to the accelerator pump).
When the diaphragm won't hold vacuum the rod stays low and holds the valve open. This means you are getting extra fuel.
Too much fuel thru a different passage. This is why the idle mixture screw has no affect.
So with extra fuel you need extra air. The only way to get that is to open the throttle by turning the idle speed screw in.
Usually this means the car won't start on the baseline carb settings or when adjusted when everything is alright. So you turn the idle speed screw to open the throttle to get more air in. This exposes more progression holes and the car starts (roughly and richly) usually I end up at 1100 rpm or so.
It doesn't sound like that is your issue unless you had to mess with the idle speed screw to get it to start again.

The choke could be hanging up on you, too. Make sure it is completely off the choke cam when warm
The choke can be out of adjustment, poor electrical feed/ground, or even the cam parts are sticking.
 

·
Registered
Joined
·
1,060 Posts
Last question first, yes that’s the float bowl, I’ve never understood why Weber had the brass float bowl vent on the smog legal 32/36 when the fuel is obviously open to the atmosphere as shown on your picture.

Now to the “where do I take my vacuum reading” question. Two places, to get the reading on the engine at idle use the port where the retard hose is on the manifold vacuum tee.
The ported vacuum connection (which looks right on your advance distributor hose connection) only need be used when setting up the idle adjustments on the carburetor. There’s not supposed to be any vacuum present there if properly set up, that said I ran my low compression 1.9 for decades cheating on my idle speed screw, turning it in 2-3 turns. I no longer have things set up like that. I have zero vacuum on the ported connection which is above the throttle plate.

It’s harmless to plug off both vacuum lines to the distributor, if you think the advance diaphragm is ruptured or leaking. I usually cut the rubber & plug them at the carburetor with a golf tee. That will help narrow down what could be a vacuum leak.

Finally, since you had the cover off to reset the float height I thought it would be a good time to check the operation of the power valve diaphragm & spring. Before I read Bob’s way of testing it, I used to just suck on the little hole and if it kept the vacuum it was good. Now days I’m overly geeky about numbers I guess, I like to know exactly where everything is at. No need to get heavily into all that, if you don’t do any engine or carburetor mods.

Try blocking off the two little vacuum lines to the distributor and see how it runs.
 

·
Registered
Joined
·
102 Posts
Discussion Starter · #10 ·
I guess the first thing to say is that it's not really the power valve that goes bad. Technically the power valve is in the bottom of the fuel bowl and the part that typically fails is the rubber diaphragm on the actuating rod/spring. But it's still called the power valve.

The power valve diaphragm can get a crack or hole and won't hold vacuum.
When the motor is running the vacuum pulls the power valve actuating rod up off the valve letting the valve close. When you accelerate your vacuum decreases letting the rod lower and open the valve to enrich the fuel mixture (this is in addition to the accelerator pump).
When the diaphragm won't hold vacuum the rod stays low and holds the valve open. This means you are getting extra fuel.
Too much fuel thru a different passage. This is why the idle mixture screw has no affect.
So with extra fuel you need extra air. The only way to get that is to open the throttle by turning the idle speed screw in.
Usually this means the car won't start on the baseline carb settings or when adjusted when everything is alright. So you turn the idle speed screw to open the throttle to get more air in. This exposes more progression holes and the car starts (roughly and richly) usually I end up at 1100 rpm or so.
It doesn't sound like that is your issue unless you had to mess with the idle speed screw to get it to start again.

The choke could be hanging up on you, too. Make sure it is completely off the choke cam when warm
The choke can be out of adjustment, poor electrical feed/ground, or even the cam parts are sticking.
Thank you for the detailed reply, this is very helpful. I had the airhorn off once so I'll do it again to check the power valve. The choke is another issue, but for the opposite reason you mention. It opens fine; the choke plates don't close enough when the engine is cold. Here in NorCal the weather isn't extreme and my wife doesn't drive the car when its very cold out (which is high 30's - low 40's; I know, it's all relative) so adjusting the choke is further down the to-do list.
 

·
Registered
Joined
·
102 Posts
Discussion Starter · #11 ·
Last question first, yes that’s the float bowl, I’ve never understood why Weber had the brass float bowl vent on the smog legal 32/36 when the fuel is obviously open to the atmosphere as shown on your picture.

Now to the “where do I take my vacuum reading” question. Two places, to get the reading on the engine at idle use the port where the retard hose is on the manifold vacuum tee.
The ported vacuum connection (which looks right on your advance distributor hose connection) only need be used when setting up the idle adjustments on the carburetor. There’s not supposed to be any vacuum present there if properly set up, that said I ran my low compression 1.9 for decades cheating on my idle speed screw, turning it in 2-3 turns. I no longer have things set up like that. I have zero vacuum on the ported connection which is above the throttle plate.

It’s harmless to plug off both vacuum lines to the distributor, if you think the advance diaphragm is ruptured or leaking. I usually cut the rubber & plug them at the carburetor with a golf tee. That will help narrow down what could be a vacuum leak.

Finally, since you had the cover off to reset the float height I thought it would be a good time to check the operation of the power valve diaphragm & spring. Before I read Bob’s way of testing it, I used to just suck on the little hole and if it kept the vacuum it was good. Now days I’m overly geeky about numbers I guess, I like to know exactly where everything is at. No need to get heavily into all that, if you don’t do any engine or carburetor mods.

Try blocking off the two little vacuum lines to the distributor and see how it runs.
Thank you very much, this is really good info. It's all about the learning curve. On the Eddy carb you can pull the plug from the manifold vacuum port and the idle isn't affected very much. On the Opel the engine dies so I have to hook up the vacuum pump before starting the car.
You and Opelbits are on the same page with the power valve so that will be tested this weekend. I'll block off the vacuum lines and redo the the best-lean idle process.
 

·
Detritus Maximus
Joined
·
2,993 Posts
Thank you for the detailed reply, this is very helpful. I had the airhorn off once so I'll do it again to check the power valve. The choke is another issue, but for the opposite reason you mention. It opens fine; the choke plates don't close enough when the engine is cold. Here in NorCal the weather isn't extreme and my wife doesn't drive the car when its very cold out (which is high 30's - low 40's; I know, it's all relative) so adjusting the choke is further down the to-do list.
I don't think I'd assume that the choke isn't the problem just because the choke doesn't close enough. Unless I recall incorrectly (like that's never happened...), there is the choke spring setting (that is the adjustment made by turning the plastic cover over the choke bimetallic spring) and the choke cam. If the choke spring is not adjusted correctly, the plates will not be open enough, open too much or too slowly/too fast. Not to mention if there is an electrical problem and not doing anything.
The choke cam is what holds open the throttle plates.
So you have two separate things to check.
Proper operation of the choke spring and proper disengagement of the choke cam and throttle lever. If the choke plates are fully open when warm, then I would have a look at the choke cam, choke cam setting screw and the throttle lever/idle speed screw.
Also, now that I am reminded of it, where the ball stud attaches to the throttle shaft, if that backs off or is loose in any way, the washer (the one with the internal flats to match the flat sides of the throttle shaft) can move out and cause binding that prevents the throttle from closing completely.
 

·
Registered
Joined
·
102 Posts
Discussion Starter · #13 ·
The choke is probably opening too quickly. Also I just traced the electric choke wire and the PO hooked it to the + coil terminal so it's only pulling ~9.4V. I need to move it to a switched power source.
And you're correct, the washer fell off with the ball stud. I don't remember seeing one on OGTS but I'll look again. And I used a paper clip to secure the linkage socket to the new ball stud.
 

·
Registered
Joined
·
1,060 Posts
The choke is probably opening too quickly. Also I just traced the electric choke wire and the PO hooked it to the + coil terminal so it's only pulling ~9.4V. I need to move it to a switched power source.
And you're correct, the washer fell off with the ball stud. I don't remember seeing one on OGTS but I'll look again. And I used a paper clip to secure the linkage socket to the new ball stud.
That’s a common mistake to get power from the coil for the choke. That will screw up the functioning of the choke as Opelbits just mentioned. I just run another wire from the fuse box for mine.

After you get that sorted out plug off both vacuum lines and see how she runs. There’s a good chance that’s all you’ll need to do (aside from your linkage issue). If it still doesn’t run right proceed to the power valve inspection.

Treat your distributor canister problems as a separate issue, be certain the hoses or lines have no cracks etc. I’m finally home more now since it’s the weekend and I’ll look for a spare canister. I took one of my distributors apart and cut the shaft to prime the engine oil on my 2.0 I just can’t remember if I had a good one for that distributor. Good luck
 

·
Registered
Joined
·
1,060 Posts
On the advance distributor canister if all else fails try Todd at Opels Unlimited, hopefully someone here has a spare advance canister and will save you the grief of the wait, he’ll come through but is usually slow in my experience. I’ll look when I get home to see what I have. Another person to try in our group is Opelmiester, he’s got a fair amount of used parts. Just look him up and send him a pm.
I checked the distributor shelf and unfortunately the xtra canister I have I’m sorry to say also has a small leak in the diaphragm. I guess I’ve been holding on to it in hopes that could be repaired and forgot about it’s condition. Try the other suggestions or sometimes Facebook is worth a try
 

·
Detritus Maximus
Joined
·
2,993 Posts
When you plug off the vacuum lines, disconnect the brake booster hose at the manifold and plug the manifold. Even the booster or hose can leak.
 

·
Registered
Joined
·
102 Posts
Discussion Starter · #17 ·
I checked the distributor shelf and unfortunately the xtra canister I have I’m sorry to say also has a small leak in the diaphragm. I guess I’ve been holding on to it in hopes that could be repaired and forgot about it’s condition. Try the other suggestions or sometimes Facebook is worth a try
Thanks for looking. Last night I plugged the vacuum lines and carb ports and redid the lean-best idle process. Both the idle screw and mixture screw are about the same as they were, and vacuum from the advance port is still at 4" @ 850 rpm. Next stop is the power valve. The engine is actually idling smoothly and the car drives fine; it's just very rich.
 

·
Registered
Joined
·
1,060 Posts
Did I mention that the vacuum at the carburetor port should be zero?
What happens there is you end up dumping more fuel from the progression holes at idle into the engine, that’s what happens if you have your idle speed screw turned in more than 1 1/2 turns from contact with the throttle stop.
If it’s running rich just at idle you might look at that.

This scenario wouldn’t cause you to run rich at acceleration or cruise, just too rich when your foot is off the gas.

To get the true engine vacuum reading at idle it should be taken off of the manifold. If you’re interested in getting that reading. I’m having a difficult time understanding why you are taking vacuum readings from the carburetor port.
 

·
Registered
Joined
·
102 Posts
Discussion Starter · #20 ·
Did I mention that the vacuum at the carburetor port should be zero?
What happens there is you end up dumping more fuel from the progression holes at idle into the engine, that’s what happens if you have your idle speed screw turned in more than 1 1/2 turns from contact with the throttle stop.
If it’s running rich just at idle you might look at that.

This scenario wouldn’t cause you to run rich at acceleration or cruise, just too rich when your foot is off the gas.

To get the true engine vacuum reading at idle it should be taken off of the manifold. If you’re interested in getting that reading. I’m having a difficult time understanding why you are taking vacuum readings from the carburetor port.
Yes you did, and I was reading the carb port just to verify if the idle holes were still uncovered after I redid the lean-best idle procedure. At 1 1/2 turns (and 2 1/4 turns out on the mixture screw) the engine only idles at ~650 (vacuum at <1"). To increase idle rpm to ~850 and smooth it out requires 2 turns in, which then increases the vacuum to 4".
The manifold vacuum is another issue. With the carb port blocked (and both distributor ports blocked), manifold vacuum flutters between 16" - 20". Turning the idle screw in another 1/4 turn (now at 2 1/4 turns) the rpm increases to ~1000, vacuum holds steady at 21", but the carb port vacuum also increases.
So isolating the carb from both distributor diaphragms seems to indicate the vacuum leak is at the carb, or even the brake booster as Opelbits mentioned.
As I understand, I'm shooting for ~850 idle rpm (warm, choke off), 0" carb vacuum, and ~20" manifold vacuum. Is that about right?
 
1 - 20 of 25 Posts
Top